JPH05290158A - Skeleton line vectorization processing method for image data - Google Patents

Abstract

PURPOSE:To provide the method deciding parallelism without using any subjective parameter, in consideration of the difficulty in setting an intersection permissible range as a criterion for deciding whether or not skeleton line vectors are parallel in skeleton line vector connection processing. CONSTITUTION:A point M to be processed as an object of reference line setting and a comparison point N are selected. Data on outline data AA', BB', CC', and DD' used to generate interruption points M and N are obtained. Mid-points S and T of the segments AD and BC are set and the length of the segment ST is found. The lengths of the segments AB and CD are found and compared with each other. The lengths of the shorter segments AB and ST are compared. When ST >= AB, it is decided that the cores M and N are parallel. The segment MN is regarded as the reference line of the point M to be processed. The intersection of the reference lines MN and KL which are thus obtained is regarded as a connection point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method based on image vectorization processing, and more particularly to a technique for connecting core line vector break points.

[0002]

2. Description of the Related Art In recent years, with the spread of CAD (Computer Aided Design), the need for drawing input devices has increased. The drawing input device is used to read an image such as a drawing or a document with an image scanner or the like to obtain image data suitable for handling by CAD or the like.
It is important to perform data compression while ensuring the ease of handling in such cases. An image processing technique that satisfies these points is image vectorization processing. In this image vectorizing process, the binarized image data read from an image scanner or the like is processed, the contour of the image is extracted to generate a contour vector, and the contour vector is used to generate a core line vector. The obtained vector data is used for a recognition process or the like in which basic elements (characters, line segments, etc.) that form an image are separated and coded.

Here, the skeleton vectorization process of the image (skeleton vector generation process) will be described. FIG. 14 shows an outline of the procedure for the core vectorization process. In addition, FIG.
An example of an image to be processed is shown, (a) is a read image (original figure), (b) is an image at the time of core line vector generation,
(C) shows an image after connecting the core vector. In this process, first, the line information is structured so that the contour vector data can be searched at high speed (S1), and then the core line vector generation process is performed (S2). That is, the contour vector 1 forming two pairs is searched for, and the core line vector 2 corresponding to the center line of the pair of contour vectors 1 is generated. This process is continuously performed along the contour, and when the contour vector pair is interrupted, the point is stored as the interruption point 3 and the search for a new contour vector pair is started. When the generation of the skeleton vector 2 is completed, the information of the break point 3 is structured so as to be easily handled (S3), and the connection point 4 is set to connect the predetermined break point (S4). Further, the section of the core wire is reorganized according to the result of the interruption point connection processing, and the plurality of connected core wire sections are integrated into one (S5).

In the above-described core line vector generation, the processing accuracy of the break point connection has a great influence on the quality of the image of the processing result.
As an example of conventional break point connection processing, Japanese Patent Laid-Open No. 3-7478
The technology described in Japanese Patent Publication No. 1 is cited. When extracting the break points to be connected, the break points and the end points of the contour vector are connected by a predetermined reference to create a loop corresponding to the outline of a branch point or an intersection. However, the breakpoints belonging to a single loop are integrated into one, which enables highly accurate breakpoint connection processing.

After that, the position of the connection point connecting the interruption points is set. In this setting, since the branch points and the intersections often include straight lines, the parallel core lines are recognized and they are connected to each other. It is important to handle so that the core wires of are connected linearly. In the above conventional technique, as shown in FIG. 16, the core line vector to be connected is LL ′,
MM ', NN', the interruption points of each core wire are L, M, N respectively.
Then, the intersections A, B, of the straight lines LL ', MM', NN '
Taking C, it was determined whether or not each core wire was parallel based on each intersection angle. That is, one of the intersection angles, for example, the intersection angle of the straight lines MM ′ and NN ′ is 180 ° ±
If α (α is a set angle) is within the range, it is determined that the core lines MM ′ and NN ′ are parallel to each other, and the intersection point between the straight line MN and the straight line LL ′ is obtained and set as the connection point R (pattern. 1). If any of the intersection angles is out of the range of 180 ° ± α, the center of gravity of the triangle ABC is obtained and used as the connection point R (pattern 2).

[0006]

In the above-mentioned conventional technique, the position of the connection point is considerably different depending on which one of the patterns 1 and 2 is applicable. Therefore, in order to improve the processing accuracy, a parameter for pattern determination is used. Proper setting of a certain angle α is important. However, since the angle α is a value that is subjectively determined, there is no choice but to take a method of optimizing α by trial and error, and it is difficult to optimally set the angle α. This is one of the factors that hinder the accuracy of the image vectorization process and increase the burden on the operator.

In view of such circumstances, it is an object of the present invention to provide a method for determining the position of a connecting point of a core wire that can obtain an appropriate position without using subjective parameters. ..

[0008]

Means and Actions for Solving the Problems
The contour vector pair is traced and the core line vector is continuously set at the center of the contour vector pair, and at the discontinuity portion of the contour vector pair, the end point of the core line vector is set as an interruption point. A method of extracting a group of discontinuity points to be connected to one of the discontinuity point groups, obtaining connection points of core line vectors for each of the discontinuity point groups, and integrating the core lines. In the method of extracting the interruption points of, the reference line connecting the interruption points and setting the position of the connection point using the reference line, a pair of interruption points in which the core lines are parallel to each other are extracted. At the beginning,
Take the following steps:

That is, first, the position data of the four end points of the two contour vector pairs used when the two suspension points are generated are loaded from a predetermined file. Assuming a quadrilateral with these four endpoints as vertices, and letting two sides having an interruption point among the sides of this quadrilateral be side sides and the other two sides being upper and lower sides, the length of both side sides and the upper and lower sides are defined. Find the length of the auxiliary line that connects the midpoints. After that, the length of this auxiliary line is compared with the shorter one of both sides, and when the auxiliary line is longer or the lengths of both sides are equal, it is determined that the core lines at the interruption point are parallel to each other. ..

Explaining the basis of this criterion, when the core lines corresponding to the respective interruption points are in a positional relationship where they intersect at a large intersection angle, the above quadrangle takes a shape close to a trapezoid with both sides as legs. , The auxiliary line is shorter than both sides. On the other hand, if the cores intersect with a small crossing angle, that is, if they are close to parallel, the above quadrilateral takes a trapezoidal shape with bases on both sides or a shape close to a rectangle. The line gets longer. From this, it is understood that the size relationship between the auxiliary line and the side is the reference for parallel determination.

This method of treating the core wire is suitable for use in the following apparatus. That is, the reference line setting means for setting the reference line corresponding to each interruption point in the pending point group, and the connection point of the core line vector based on the number and the positional relationship of the reference lines set in the pending point group. The image processing apparatus includes a connection point setting unit for setting.

Here, the reference line setting means has the following means.

(1) Concerning a pending break point It is judged whether or not there is a break point in which core lines are parallel to each other in the break point group,
Reference line generation processing selection means for selecting the reference line generation means based on this determination result. This reference line generation processing selection means is
It has the following means. a) Data fetching means for fetching the position data of the end points of the contour vector pair corresponding to the two interruption points to be judged. b) Calculation means for calculating the length of both sides of the quadrangle and the length of an auxiliary line formed by connecting the midpoints of the upper and lower sides. c) A determining means that compares the length of the auxiliary line with the lengths of both sides and determines whether or not the core lines at the interruption points are parallel to each other based on the comparison result.

(2) A first reference line generating means which is selected when there is an interruption point where the core lines are parallel to each other and which uses the connection line of the interruption point and the suspension point as a reference line.

(3) Second auxiliary line generating means which is selected when there is no break point at which the core lines are parallel to each other and which uses a straight line corresponding to an extension line of the core line of the pending break point as a reference line.

(4) Searching means which operates after the reference lines are set at all the interruption points in the pending interruption point group and searches for the interruption points which are the end points of the plurality of reference lines as the reference line limitation candidate points. ..

(5) The operation is performed when there are a plurality of reference line limitation candidate points, and the number of reference lines relating to each reference line limitation candidate point is limited to one, respectively. Reference line limiting means for selecting a reference line having the smallest intersection angle with the core line as a reference line to be left.

On the other hand, the connection point setting means has the following means.

(1) Connection point generation processing selection means for selecting connection point generation means based on the number of reference lines.

(2) A first connection point generating means which is selected when the number of reference lines is one and uses the midpoint of the reference line as the connection point.

(3) A second connection point generating means which is selected when the number of reference lines is two and which has connection points at the intersections of the reference lines.

(4) A third connection point is selected when three or more reference lines are selected, and three reference lines are selected and the points inside the triangle having their intersections as vertices are the connection points. means.

[0023]

Embodiments of the present invention will be described below.

FIG. 2 shows a main part of the system configuration of the image processing apparatus according to the embodiment of the present invention. Reference numeral 4 is an input interface for receiving inputs from the pointing device 5 and the like, 6 is a CRT (cathode ray tube) device, 7 is a display interface for display control, 8 is an external storage device, 9 is an external storage interface, and 10 is an external system. Reference numeral 11 denotes a CPU (central processing unit), which is a communication control interface for transmitting image data and the like. Reference numeral 12 is a main memory, which stores the core vectorization processing and other programs according to this embodiment. As described above, in the skeleton vectorizing process, a skeleton vector including a discontinuity (interruption point) is generated, and after that, a discontinuation point connection process is performed to connect discontinuities in the skeleton vector. In this break point connection processing, first, the plurality of break points obtained in the preceding process are grouped into those that should be connected into one, and the position of the connection point is calculated using the data regarding each group. In this embodiment, first, a reference line corresponding to an extension of the core wire is set for each interruption point in consideration of the positional relationship with other core wires, and then the position of the connection point is calculated using this reference line. I am going to do it.

The outline of the reference line setting processing procedure is shown in FIG.
An example of setting the reference line is shown in FIGS. Explaining using the example of FIG. 3, first, the CPU selects one interruption point (hereinafter referred to as a processing target point) as a reference line setting target from the target interruption point group, and at the same time, determines another interruption point ( One of the comparison points will be selected (S1). Assuming that the interruption point M is selected as the processing target point and the interruption point N is selected as the comparison point, the data of the contour vectors AA ′, BB ′, CC ′, DD ′ used for generating the interruption points M, N are obtained next. Obtain (S2). As the data on each break point, the data of the contour vector used when the break point is generated is prepared in advance. Then, it is determined whether or not the core lines M and N are parallel using the acquired contour vector data (S
3).

In this determination, first, the midpoints S and T of the line segments AD and BC are taken and the length of the line segment ST is obtained. Next, line segment A
The lengths of B and CD are obtained and the lengths are compared.
Then, the length of the shorter one (here, the line segment AB) and the length of the line segment ST are compared. As a result, if ST ≧ AB, it is determined that the cores M and N are parallel, and if ST <AB, it is determined that the cores M and N are not parallel.

When the cores M and N are parallel (S4: Ye
s), the line segment MN is taken and set as the reference line of the processing target point M (S5). If the core lines M and N are not parallel (S4: No), another interruption point is searched for and selected as a comparison point (S6, 7), and parallel determination is performed again to set a reference line for the processing target M.

Here, as shown in FIG. 4, when no comparison point is selected, there is no combination in which the core lines are parallel (S6:
No), the reference line is set by the following procedure (S8). Assuming that the processing target point is M, the interruption point N is first selected as a comparison point. Then, the angles on the side where the core vector of the contour vector at the contour vector end points A and B corresponding to the processing target point M is present (here, ∠A′AD (superior angle), ∠B′BC.
(Inferior angle)). Next, the sizes of ∠A′AD and ∠B′BC are compared and the smaller angle (∠B′BC) is selected. Then, a straight line AA ″ that makes the same angle as ∠B′BC with respect to the contour vector AA ′ is taken, the intersection point P of the straight lines AA ′ and BC is obtained, and the line segment MP is set as the reference line of the processing target point M. Also for the processing target point N, the reference line NQ
To set.

In this way, the reference line is sequentially set for each interruption point (S9, 10), and when the reference lines have been set for all the interruption points (S10: No), the reference line is arranged if necessary. Then proceed to the connection point calculation. That is, first, the break point which is the end point of the plurality of reference lines is detected,
If there is no such interruption point or if there is only one (S11: No), the reference line setting process is terminated without performing the reference line arrangement. If there are a plurality of break points satisfying the above condition (S11: Yes), the reference line is arranged (S12). In the example shown in FIG. 5, L and M are break points that satisfy the above conditions. Explaining the interruption point L, the reference lines having the interruption point L as an end point are line segments LM and LN. Therefore, the crossing angles of the line segments LM and LN with respect to the contour vector CC '(or DD') are obtained and their sizes are compared. Then, the line segment LM having a small intersection angle (approximately 0 °) is left as the reference line, and the reference line LN is deleted. Similarly, for the interruption point M, the reference line KM is deleted. As a result, the reference line is organized into two line segments JP and LM.

After that, the connection point is calculated using the reference line obtained as described above. The outline of the connection point calculation procedure is shown in FIG. Further, examples of connection point calculation are shown in FIGS. In this process, the CPU first confirms the number of reference lines (S
1) Select a predetermined calculation method according to the number. That is, when the number of reference lines is one, as shown in FIG. 7, the midpoint of the reference line MN is obtained and set as the connection point R (S2). When the number of reference lines is two, the intersection of the two reference lines is obtained and set as the connection point R as in each example of FIGS. 8 to 12 (S3). Baseline is 3
In the case of a book, as shown in FIG. 13, reference lines KN, JM, L
The points U, V, W at which O intersects with each other are obtained.
The center of gravity of a triangle having V and W as vertices is calculated and set as the connection point R (S4). In addition, when three reference lines intersect at one point,
The intersection is defined as the connection point R. If there are 4 or more reference lines,
After selecting 3 lines from the reference line (S5), the reference line is 3
As in the case of the book, the center of gravity of the triangle at the intersection is used as the connection point. In selecting the three reference lines, the intersection angle between the reference lines is first obtained, and the pair of reference lines having the closest intersection angle of 90 ° is obtained. Then, one reference line is selected from this pair, and the reference line whose intersection angle with the selected reference line is closest to 45 ° is obtained. This gives a combination of the three reference lines whose intersection triangle is closest to the isosceles right triangle. A connection point is obtained using the three reference lines thus obtained.

[0031]

As described above, according to the present invention,
When connecting skeleton vectors, in deciding whether or not skeletons are parallel to each other, a quadrangle having four endpoints of two contour vector pairs used at the time of generating two suspension points as vertices is assumed, The size of the auxiliary line in the shape and the size of the predetermined side is used as the criterion. Therefore, since it is possible to determine the parallelism of the core lines without considering the intersection angle of the core line vectors,
It is not necessary to set the allowable range of the intersection angle. Therefore, it is possible to eliminate a decrease in processing accuracy and an increase in operator's burden due to the setting of the allowable range of the intersection angle.

[Brief description of drawings]

FIG. 1 is a flowchart showing an outline of a reference line setting procedure according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a main part of a system configuration of the image processing apparatus according to the embodiment of FIG.

FIG. 3 is an explanatory diagram showing a reference line setting example.

FIG. 4 is an explanatory diagram showing a reference line setting example.

FIG. 5 is an explanatory diagram showing a reference line setting example.

FIG. 6 is a flowchart showing an outline of a connection point calculation procedure.

FIG. 7 is an explanatory diagram showing a connection point setting example.

FIG. 8 is an explanatory diagram showing a connection point setting example.

FIG. 9 is an explanatory diagram showing a connection point setting example.

FIG. 10 is an explanatory diagram showing a connection point setting example.

FIG. 11 is an explanatory diagram showing a connection point setting example.

FIG. 12 is an explanatory diagram showing a connection point setting example.

FIG. 13 is an explanatory diagram showing a connection point setting example.

FIG. 14 is a flowchart showing an outline of a skeleton vectorizing process procedure.

FIG. 15 is an explanatory diagram showing an example of an image.

FIG. 16 is an explanatory diagram showing a conventional connection point setting example.

[Explanation of symbols]

 1 ... Contour vector 2 ... Core vector 3 ... Interruption point 5 ... Pointing device 6 ... CRT 8 ... External storage device 10 ... Communication control interface 11 ... CPU 12 ... Main memory

Claims (1)

[Claims] 1. A contour vector pair is traced to continuously set a core line vector at the center of the contour vector pair, and at the discontinuity portion of the contour vector pair, an end point of the core line vector is set as an interruption point. A method of extracting a group of interruption points to be connected to one of the interruption points, obtaining connection points of the core line vector for each of the interruption points, and integrating the core lines. In the method of extracting a pair of break points that are parallel to each other and obtaining a reference line formed by connecting the break points, and setting the position of the connection point using this reference line. In extracting a break point, position data of four endpoints of two contour vector pairs used when generating two pending break points is prepared, and the break point of the sides of the quadrangle having the four endpoints as vertices. Having 2
If the side is the side and the other two sides are the upper and lower sides, the length of both sides and the length of the auxiliary line formed by connecting the midpoints of the upper and lower sides are calculated. Of the auxiliary line is longer or the lengths of the two are equal to each other, it is determined that the core lines at the interruption point are parallel to each other.